The present invention relates to a material for a color picture tube shadow mask and a color picture tube using the same.
A conventional color picture tube shadow mask has a large number of regularly aligned apertures. The number of electrons passing through the apertures is about 1/3 or less the total number of electrons. The remaining electrons bombard and heat the shadow mask, resulting in thermal expansion of the shadow mask and degradation of color purity.
In a conventional color picture tube with a shadow mask, beam mislanding caused by thermal expansion must be limited. For this reason, improvements in the shadow mask structure itself, the assembly of the shadow mask and its support, and the shadow mask material have all been explored. However, no substantial solutions have been found so far.
Mild steel is normally used as a shadow mask material. Although mild steel has good press formability, its thermal expansion coefficient is as high as 12.times.10.sup.-6 /.degree. C. Thus thermal deformation occurs upon electron beam irradiation, and color purity is degraded
In order to prevent thermal deformation, an Fe-Ni invar alloy shadow mask with a small thermal expansion coefficient has been proposed Since this alloy has a high yield stress, however, it provides poor press formability. In addition, since the invar alloy has a low elasticity coefficient, deformation of the shadow mask can occur during fabrication, assembly of a color picture tube, and operation of the color picture tube, thus degrading color purity. Recently, various types of shadow mask materials have been proposed in, among others, Japanese Patent Prepublication Nos. 50-58977 and 59-59861. These materials are prepared by adding alloy elements to an Fe-Ni invar alloy. However, they cannot completely overcome the conventional shortcomings.